1. Field of the Invention
The present invention relates to a pressure vessel for use under a high pressure condition.
2. Description of the Related Art
Pressure vessels designed to withstand high operating pressures have heretofore been known such as, for example, pressure vessels for petrochemical plants and nuclear reactor pressure vessels.
A pressure vessel described in Japanese Utility Model Laid Open No. Hei 6 (1994)-49898 has a vessel body and a nozzle projecting from the vessel body in a direction perpendicular to an inner surface of the vessel body. The pressure vessel described therein is provided with a through hole of a circular section extending through both the pressure vessel and nozzle in a direction perpendicular to the inner surface of the vessel body.
There also is known a pressure vessel having an inclined nozzle projecting from a vessel body in a direction inclined relative to an inner surface of the vessel body. The inclined nozzle indicates a nozzle extended in a direction not perpendicular to the inner surface of the vessel body. The pressure vessel in question is provided with a through hole of a circular section extending through both the vessel body and nozzle in a direction inclined relative to the inner surface of the vessel body (in the projecting direction of the inclined nozzle from the vessel body).
A peak stress induced in the pressure vessel under a predetermined pressure condition is larger in the pressure vessel having the inclined nozzle than in the pressure vessel described in the above utility model publication which has a nozzle perpendicular to the inner surface of the vessel body. More particularly, in the pressure vessel having the inclined nozzle, since the through hole is formed inclinedly, an extremely thin wall portion (an acute-angled portion) of the vessel body is formed partially in the circumferential direction at the portion where the surface surrounding the through hole and the inner surface of the vessel body intersect with each other, and stress is concentrated on the extremely thin wall portion. Consequently, the peak stress in case of providing the inclined nozzle becomes larger than in the pressure vessel having a nozzle perpendicularly to the inner surface of the vessel body.
In the conventional pressure vessel having the inclined nozzle, the wall thickness of the vessel body is made large or the inclined nozzle is strongly reinforced to diminish the peak stress induced in the pressure vessel.
However, making the wall thickness of the vessel body large or strongly reinforcing the inclined nozzle results in increase of the amount of the material which constitutes the pressure vessel, thus leading to a marked increase of the cost.